Study of transient quantum phases of matter via light-control of dynamical charge correlations

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We often identify quantum materials as solid systems wherein strong electron interactions, in concert with low-dimensionality, lead to the emergence of phenomena unexplainable via (quasi-)classical approaches, such as superconductivity, and charge order. The scientific community has extensively studied the ground state of quantum materials in the past decades, but only very recently have we begun to develop tools for controlling the properties of materials on demand. In this regard, light-matter interaction is probably the most powerful and flexible tuning knob to control the properties of solids. Recent proof of principle demonstrations of this approach span light-induced superconductivity to photoinduced metal-to-insulator transitions.Charge order, i.e. the self-reorganization of the electronic density, is a common feature among quantum materials, and it may assume different forms ranging from long-range domains to short-range and dynamical (fluctuating) charge correlations. The later are of renewed interest as they are believed to be a fundamental ingredient (hidden until very recently) for understanding some of the technological-relevant properties of quantum materials such as superconductivity, nematicity and linear resistivity. This multi-institutional collaboration across Canada connecting INRS (Boschini), McGill University (Siwick) and QMI-UBC (Damascelli and Berciu), as well as other national and international collaborators, propose to use high-intense ultrashort light excitations (in the visible to THz range) to control the strength and spatial distribution of dynamical charge correlations in a variety of quantum materials. The importance of this project is backed by the idea that dynamical charge correlations could be a general feature of all quantum materials, arising from the specific spatial dependence of the electron interactions inside solids. In fact, while the interaction among two electrons in free space decays monotonically with distance (the well-known Coulomb's law), the electron-localization and lattice periodicity of solids may result in an effective non-monotonic Coulomb potential which may favour electron pairing and correlations. The use of light pulses precisely tailored to specific systems' energetics will allow us to transiently change the lattice structure along specific crystallographic directions, as well as tune the on-site electron-electron screening to lock or dissolve dynamical charge correlations in an ultrafast fashion. Not only will this study offer brand-new information on the microscopic origin of dynamical charge correlations in solids, but it will establish the light-control of dynamical charge correlations as a new, generalizable approach to tune the properties of quantum matter on demand.This ambitious project will be made possible by the unique opportunity of combining complementary ultrafast techniques, such as time-resolved photoemission spectroscopy (TR-ARPES - using the two systems of Boschini and Damascelli with different working parameters), ultrafast electron diffuse scattering (UEDS - Siwick), and free-electron-laser-based x-ray scattering (TR-XRS - Boschini). While TR-ARPES accesses fundamental electrodynamics with momentum resolution, UEDS and TR-XRS map the transient evolution of the phonon populations and lattice reconstructions. In addition, theoretical support (Berciu) will be essential to guide the interpretation of experimental data. Not only this project will grant an unprecedented peek into the dynamical properties of quantum materials, but will train highly qualified personnel in ultrafast science across Canada.